A Question of Etiquette

[flydye8]

I have been in college for a while now and have had many teachers;  I usually address my teachers as Mr./Miss/Mrs so and so and have never been corrected till today. 
I typed and email to my teacher for my World Cultures class, and his reply back to be was odd; before even answering my question he said I should address him as Professor or Doctor. 
Now I have been taught that addressing a person by Mr/Mrs/Miss was respectful and appropriate within the classroom environment; but now I wonder how many teachers I have offended by not addressing them by Doctor/Professor.
So if anyone knows the proper way to address a teacher in college please let me know so I don't offend another teacher during my tenure at my university.

Thanks